Former US Vice President Joe Biden announced Thursday he is entering the 2020 White House race, joining an already crowded list of candidates running on the Democratic Party platform.

In a tweet accompanied by a three-and-a-half minute video, Biden said he couldn't stand idly by while US President Donald Trump "fundamentally altered the character of this nation".

"The core values of this nation... our standing in the world... our very democracy... everything that has made America -- America -- is at stake," he wrote in the post.

"That's why today I'm announcing my candidacy for President of the United States."

Even before his official announcement, Biden, who served eight years as Barack Obama's vice president, led most surveys of Democratic voters.

The RealClearPolitics poll aggregate puts him as the favourite with 29.3 percent support, followed by independent Senator Bernie Sanders at 23 percent.

The core values of this nation… our standing in the world… our very democracy...everything that has made America -- America --is at stake. That’s why today I’m announcing my candidacy for President of the United States. #Joe2020https://t.co/jzaQbyTEz3